"The last time we had any definite signals of auroral activity on Uranus was when NASA's Voyager 2 probe swung by in 1986," said study leader Laurent Lamy, an astronomer at the Observatoire de Paris in Meudon, France.

"But this is the first time we can actually see these emissions light up with an Earth-based telescope."

Auroras tend to surround a planet's poles, where magnetic field lines converge and funnel incoming charged solar particles into the planet's atmosphere. There, the particles collide with air molecules, making the molecules glow.

Scientists tried unsuccessfully to detect auroras on Uranus in 1998 and 2005. In September 2011, Lamy and his team learned of an impending solar storm directed toward Uranus, which sits about 2.5 billion miles (4 billion kilometers) from Earth.

"We definitely had luck on our side to catch these faint flashes," Lamy said.

Oddball Planet May Influence Auroras

The auroras' unusual appearance might have something to do with the planet's oddball orientation.

Unlike the other seven planets, Uranus's magnetic axis is 60 degrees off from its spin axis. In addition, spin axis itself has a bizarre 98-degree tilt relative to the solar system's orbital plane. In other words, the planet seems to roll around on its side as it orbits the sun.

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